NCP1379 ON Semiconductor, NCP1379 Datasheet - Page 15

• Manufacturer Part Number: NCP1379
• Description: Quasi-Resonant Current-Mode Controller
• Manufacturer: ON Semiconductor

Time Out
comparator can be unable to detect the valleys. To avoid
such situation, NCP1379 integrates a Time Out function that
acts as a substitute clock for the decimal counter inside the
logic bloc. The controller thus continues its normal
operation. To avoid having a too big step in frequency, the
time out duration is set to 5.9 ms. Figures 30 and 31 detail the
time out operation.
the soft−start.
auxiliary winding is low. Because of the voltage drop
In case of extremely damped free oscillations, the ZCD
The NCP1379 also features an extended time out during
Indeed, at startup, the output voltage reflected on the
Figure 28. Zoom 4: 4
Figure 27. Zoom 3: 3
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th
Valley to VCO Mode Transition
rd
15
to 4
introduced by the Over Power Compensation diode
(Figure 35), the voltage on the ZCD pin is very low and the
ZCD comparator might be unable to detect the valleys. In
this condition, setting the DRV Latch with the 5.9 ms
time−out leads to a continuous conduction mode operation
(CCM) at the beginning of the soft−start. This CCM
operation only last a few cycles until the voltage on ZCD pin
becomes high enough to be detected by the ZCD
comparator.
during the soft−start in order to ensure that the transformer
is fully demagnetized before the MOSFET is turned−on.
th
To avoid this, the time−out duration is extended to 40 ms
Valley Transition
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